1. Technical Field
This invention relates generally to spark ignition devices, such as spark plugs for internal combustion engines, and more particularly to the alloys used to make the sparking surface of the sparking electrode of such devices.
2. Related Art
Various precious metal alloys are used for the sparking surfaces of spark plug electrodes. Some of the precious metal elements are less costly than others, but there is sometimes a trade-off in terms of the properties that can be achieved using the less costly alloy alternatives. For example, palladium is a relatively low cost element, however it has been found to oxidize in the operating environment of spark plug sparking surfaces. For example, the palladium used in sparking surfaces made from alloys of rhenium-palladium or platinum-palladium-iridium alloys has been shown to oxidizes during use.
It has been found that alloying gold with palladium has the beneficial effect of mitigating the oxidation of palladium under the operating environment of a spark plug electrode. However, known palladium-gold alloys (e.g., Au40Pd) have mechanical properties believed to be too soft and weak for extended use in modern sparking surface applications. Further, the known palladium-gold alloy materials are prone to alloy with the combustion constituents present in the operating environment, such as lead, thereby causing the material to degrade in use.